The differences in healthy longevity between parts of even affluent cities like London is astonishing. It is the same as between developed nations and developing nations who are experiencing war and famine. In terms of life expectancy most large city dwellers live in different worlds only a few miles apart. The differences are in the order of a decade of additional healthy lifetime! Ten more or less years of precious life.
The reasons are manifold and complex. The reason I have picked an example of the same city is to reduce many arguments such as societal and cultural differences or healthcare (the UK has a free national health service). Of course poverty (and the many ills it causes) or quality and level of education differ within a city and are contributing factors. Nutrition is also one of the main contributors as can be seen with correlations between level of obesity in the same areas where life expectancy is also lower. For example, childhood obesity ranges between 10.7% and 29.6% across the different areas of inner London.
Finding good and affordable ways to reach people who live in nutrition poverty anywhere in the world is what fiber consumption can tackle in a better and more economical way than many other well-meaning efforts (for a more detailed discussion see the book).